4chan is not in the UK and ofcom has no jurisdiction. This would be like Singapore trying to prosecute you for smoking marijuana in your own home in the U.S.
Have you ever opened 4chan? There are literally 3 threads right now with "drawn images" illegal in many countries. To me it's crazy it's still open. Early 4chan had the worst kind of images you could think of.
Being mean, for varying degrees of "mean", is actually illegal in most countries that aren't the USA and surely 4chan passes the threshold in at least some of them.